Studies on the Antibacterial Factors of Human Saliva.

In previous studies it was found that the growth of 110 of 169 strains of bacteria tested was prevented by human saliva (Bibby, Clough and Hine, 1938). This effect was more marked against some types of organisms than against others, those most affected being bacilli and cocci isolated from air and water; those least affected, organisms isolated from the mouth. Differences occurred in the inhibitory potency of saliva from individual to individual and from time to time. Dissimilarities were noted between the agent effective against Micrococcus lysodeikticus and that acting on strains of lactobacilli, streptococci, and staphylococci. The former activity was removed by Berkefeld-N filtration and appeared to be more closely associated with oral bacteria and the presence of epithelial cells. Our suggestion that there are two distinct antibacterial agents in the saliva is supported by Thompson who has summarized the evidence in an excellent review (1940) and shown (1941) differences in the properties of salivary lysozyme and another antibacterial factor in the saliva. The present study was designed to establish more definitely whether there is more than one antibacterial agent in saliva and, if so, to investigate the properties of such agents. To this end saliva was subjected to various treatments before testing against susceptible bacteria. Tests were made of its mode of action on different organisms and attempts at concentration and purification of the agents were undertaken.